Differentiating between friends has always been stressful. Remember first grade with the heart-halves necklaces? That tetherball might be aimed at your head during recess if a non-BFF was hurt that you gave the BE- FRI- side to someone else.
Instead of two categories - best friend forever, and everyone else - there are now multiple levels of friendship, all blurry. These days, there is a pyramid of friendship by communication: at the bottom you have your Gchat friends, then Facebook friends, AIM friends, and at the apex, your cell phone friends.
This is not to say the categories don't overlap; friends who are cell phone-worthy are fair game for Gchatting, too. But I feel comfortable Gchatting almost anyone. The only person I've refrained from chatting with is an old professor of mine who often pops up on my "Quick Contacts" list. But don't think I wasn't tempted.
Facebook is a bit less of a free-for-all. While being "friends" on Facebook can mean just the slightest of acquaintances ("It was great talking to you while we waited in line for the bathroom at Pi Kap!"), friending someone, sending a message, and writing on a wall still indicate a specificity of search that may intimidate Facebook prudes.
But still, Gchat and Facebook are easy, which makes AIM and cell phones all the more complicated. To IM someone, you need their screen name, which means you either steal it off Facebook or personally ask for it. No matter how many times you've stolen them, it's still awkward when you receive that initial IM: "Hey, it's Steve from Econ. How r u?" And even if you talk to Steve online for weeks, when is it okay to take it to the next level and start speaking on the phone? Forget casual to exclusive, the move from emoticons to actual, on-the-phone LOLs is a dramatic (not to mention unlikely) step.
Yet there is a benefit amidst all the confusion - that motherly admonition of "you can have more than one best friend" is finally true. After all, your cell phone does have space for at least nine speed dials. Welcome to the modern BFF test: if the speed dialing is reciprocated, you have a match!